Currently in the field of electronics, for example with semiconductor devices, charge degree of freedom of electrons are used; electrons have spin degrees of freedom, in addition to charge degree of freedom. In recent years, spintronics using spin degree of freedom have been drawing attention as a next-generation carrier for information technology.
In spintronics, the charge degree of freedom and the spin degree of freedom of electrons are simultaneously used in order to gain new functions and properties.
Spin RAMs that control the direction of magnetization of a free layer using the spin of electrons which are carriers of a current by making a current flow directly through a GMR element or a TMR element are one example of an application of spintronics (see for example Patent Document 1 and Patent Document 2).
In addition, quantum computers can be cited as another application of spintronics. In quantum computers, the spin of atoms, ions and molecules is used as quantum bits (Qubits) (see for example Patent Document 3).
Thus, it is clear that quantum calculation and quantum information storage are possible using the dynamics of spin in magnetic recording, and it is known that use of a spin current is useful for readout and control.
Currently information transmission in information processing apparatuses is carried out using electron flow, which causes Joule heat. Joule heat is a problem, in that the more the information processing unit is integrated, the higher the power consumption is, and therefore information transmission using spin current instead of electron flow has been investigated. Such information transmission is based on the use of spin current, which is a reversible process, instead of the flow of conduction electrons in a solid, which is chronologically irreversible. Since barely any spin angular momentum is dissipated, the power consumption does not increase.
Spin-Hall effect is well known in spintronics. When an electric current flows through a sample, a pure spin current is generated in a direction perpendicular to the direction of the electric current, and there is no flow of charge, and the spin polarization is accumulated at the sample edge in the direction of the pure spin current (see for example Non-Patent Document 1).
The inventors found out that when a pure spin current is injected into a sample, an electric current flows in a direction perpendicular to the direction of the pure spin current. Inverse spin-Hall effects cause a difference in potential at the end of a sample, and therefore it is possible to detect whether or not there is a pure spin current by detecting this difference in potential (see for example Non-Patent Document 2).